Joaquin Phoenix is either one of the greatest actors ever to walk the red carpet on his way to that Entertainment Tonight sound bite, or he's an insufferably neurotic, narcissistic, doped-up jerk.

Whichever turns out to be the case (I'm betting on the latter), I'm Still Here - the documentary-like chronicle of a year in the life of the twice-Oscar-nominated thespian, as he announces his retirement from movies to pursue a career as a hip-hop artist - stands as a fascinating look at the cloistered, coddled world of a movie star who's not quite up there in the A-list tier of, say, Leo or Tobey. (At one point in the film, slouched miserably in a rented minivan en route to the Obama inauguration, Phoenix bemoans the fact that DiCaprio and Maguire are probably heading to D.C. via private jet and stretch limo.)

I say "documentary-like" because it's impossible to determine where I'm Still Here is real, and where, if anywhere, it's a put-on. Like Exit Through the Gift Shop, the purported doc about street artist Banksy and his graffiti-happy cohorts, the Phoenix film has the stink of a con about it, the winky deadpan of a conceptual art piece.

Remember when the actor, nominated for an Academy Award for his portrayal of Johnny Cash in Walk the Line, guested on Late Show With David Letterman, mumbling and mussed, to plug a film (Two Lovers) he admitted he hadn't seen? Letterman reprimanded the monosyllabic Phoenix for chewing gum, mocked him for his spavined vibe, asked about his scruffy beard, and bid him a curt adieu.

The tabloids had a field day with Phoenix's Letterman stand, musing about drugs, drunkenness, and the need, perhaps, for detox. And then word got out that the celebrity actor's pal Casey Affleck was shooting the whole thing, and that they were making a movie. Hmmm . . .

Indeed, I'm Still Here has been directed by Affleck (Phoenix's brother-in-law), with a credit that reads "written and produced by Joaquin Phoenix and Casey Affleck." And that infamous Letterman appearance, which spawned a slew of snarky Phoenix parodies, is at the center of the film, a sorry spectacle that sends the actor running back to his limo, to his publicist and salaried sycophants, stopping to have a cry in the bushes of Central Park.

I'm Still Here takes the viewer from Miami to Vegas, New York to L.A. Along the way it has appearances from Ben Stiller (who drops by to see if Phoenix will reconsider his retirement for a role in Greenberg), Sean Combs (Phoenix wants "Puff" or "P-Diddy" or "Mr. Combs" - the twitchy star doesn't know what to call him - to produce his rap record), Jack Nicholson, and a shamanistic Edward James Olmos. There are VIP clubs lined with lip-smacking groupies, a pricey Manhattan loft visited by pricey Manhattan hookers, and Phoenix's hillside Los Angeles home - a home, with a pool and a recording studio, that, six months into his sequestration, he realizes he can't afford.

"I don't want to play the character of Joaquin anymore," Phoenix whines. Whether or not he continues to play that character - a line-snorting, potbellied sniveler who just happens to have starred opposite the likes of Jennifer Connelly, Gwyneth Paltrow, and Reese Witherspoon - remains the big question.

But in a way, it doesn't matter: A meditation on a life lived in the public eye, I'm Still Here is strange, riveting, and occasionally appalling stuff, any way you look at it.

I'm Still Here ***1/2 (out of four stars)

Directed by Casey Affleck. With Joaquin Phoenix, Casey Affleck, Edward James Olmos, Ben Stiller, and others. Distributed by Magnolia Pictures.

Running time: 1 hour, 47 mins.

Parent's guide: No MPAA rating (profanity, nudity, drugs, adult themes)

Playing at: Ritz at the BourseEndText